The present disclosure relates to a power conversion mode control apparatus and method of a bi-directional DC-DC converter, and a bi-directional DC-DC converting apparatus including the power conversion mode control apparatus.
A hybrid electric vehicle (HEV) that uses an electric motor together with an existing internal combustion engine as a power unit has a bi-directional DC-DC converter which is operated in a boost mode or a buck mode between a battery of 48V, which is a high voltage battery and a battery of 12V, which is a low voltage battery.
An entire power system of the HEV includes a motor taking charge of an engine starting and regenerative braking, an inverter taking charge of a motor driving and regenerative power control, a high voltage battery used as an apparatus for an inverter driving and spare energy storage, a low voltage battery for driving an electric load, or the like, and a bi-directional DC-DC converter, which is a bi-directional power transfer medium between the high voltage battery and the low voltage battery.
The bi-directional DC-DC converter must be able to freely convert and transfer power in a bi-direction between a high voltage and a low voltage and needs to quickly and seamlessly implement a mode switching under various situations. Particularly, the bi-directional DC-DC converter needs to operate in a boost mode in order to implement a pre-charge at the time of an initial starting and quickly perform a switching of a power conversion mode into a buck mode after the pre-charge ends. In addition, the bi-directional DC-DC converter is operated in the boost mode even at the time of assisting in torque and transfers energy of a high voltage side to a low voltage side in other situations.
In the existing bi-directional DC-DC converter, if an external electric control unit (ECU) or a higher instructor determines a current power conversion mode and then instructs the DC-DC converter through CAN communication, the converter is passively operated in the boost mode or the buck mode by external instructions.
The bi-directional DC-DC converter which is operated by the instructions through the external CAN communication generates duty command for the low voltage side and the high voltage side, respectively, and is operated in the buck mode or the boost mode by selecting final duty command matched to the instruction when the external instruction is input to the DC-DC converter through the CAN communication.
Since the power conversion mode switching method determines a direction of the power conversion depending on the external instruction, in the case in which an external higher controller is broken down, the power conversion in a desired direction is not performed. In addition, a predetermined calculation time is required while the higher controller determines the buck mode or the boost mode from a voltage or current sensed value of the low voltage side or the high voltage side at the time of the mode switching, and a time lag occurs when the instruction is transferred to the converter by the CAN communication. Therefore, it is difficult to seamlessly and naturally switch the mode due to a sharp variation in the load at the time of the mode switching.
The following Related Art Document (Patent Document 1) relates to a bi-directional non-insulating DC-DC converter capable of reducing a current ripple of an inductor because a current of the inductor is operated in a continuous conduction mode (CCM), reducing switching loss and increasing a switching frequency by achieving a soft switching, removing a voltage surge due to reverse recovery characteristics of a diode by a soft switching operation, and making a rated voltage of the switch and the diode smaller than an output voltage.